The just released Microsoft Standalone System Sweeper, a recovery tool that can help you start an infected PC and perform an offline scan to help identify and remove rootkits and other advanced malware.
In addition, Microsoft Standalone System Sweeper can be used if you cannot install or start an antivirus solution on your PC, or if the installed solution can’t detect or remove malware on your PC.
It is particularly useful for detecting and disinfecting malware infections which give regular AV products running within Windows a hard time.
http://connect.microsoft.com/systemsweeper